Recruitment of coregulator complexes to the beta-globin gene locus by TFII-I and upstream stimulatory factor.

Upstream stimulatory factor and TFII-I are ubiquitously expressed helix-loop-helix transcription factors that interact with E-box sequences and or initiator elements. We previously demonstrated that upstream stimulatory factor is an activator of beta-globin gene expression whereas TFII-I is a repressor. In the present study, we demonstrate that upstream stimulatory factor interacts with the coactivator p300 and that this interaction is restricted to erythroid cells expressing the adult beta-globin gene. Furthermore, we demonstrate that Suz12, a component of the polycomb repressor complex 2, is recruited to the beta-globin gene. Reducing expression of Suz12 significantly activates beta-globin gene expression in an erythroid cell line with an embryonic phenotype. Suz12 also interacts with the adult beta-globin gene during early stages of erythroid differentiation of mouse embryonic stem cells. Our data suggest that TFII-I contributes to the recruitment of the polycomb repressor complex 2 complex to the beta-globin gene. Together, these data demonstrate that the antagonistic activities of upstream stimulatory factor and TFII-I on beta-globin gene expression are mediated at least in part by protein complexes that render the promoter associated chromatin accessible or inaccessible for the transcription complex.